Many commercial cellular handsets require multi-band operation. Typically, a 2G/3G cellular transceiver may cover a number of 2G frequency bands (e.g., 850, 900, 1800, and 1900 MHz) and several 3G frequency bands (e.g., bands I, II, III). The existing multi-band approach may be inefficient in terms of cost and area. The limitation of such multi-band approach may stem from the need for highly selective radio-frequency (RF) filters, such as SAW filters for 2G and duplexers for 3G operation. With the introduction of new technologies such as 4G and multiple antennas, and the demand to cover more frequency bands, the number of required RF filters and duplexers may increase to an impractical level, in terms of cost and area.
An optimal implementation of a multi-band transceiver may include an antenna-ready radio, completely integrated on a single CMOS chip. One of the missing pieces to realize the single CMOS chip antenna-ready radio is a wideband multi-band RF duplexer, for example, a wideband integrated RF duplexer supporting 3G/4G (e.g., supporting bands, such as bands I, II, III, IV, and IX). The RF duplexer may provide isolation in transmit (TX) band to avoid saturation of the receiver, and also to relax the linearity and phase noise requirement of the receive (RX) path. For CMOS implementation, a proper choice for duplexer of an RF transceiver may include an electrical balanced duplexer (EBD) with a passive balancing network. The resistor elements of the passive balancing network may generate noise that may couple to the receive (RX) path of transceiver, thereby contributing to the noise figure (NF) of the RX path.
Therefore, the need exists for a low-loss RF duplexer that can substantially cancel the noise generated by the balancing network to improve the RX path signal-to noise ratio (SNR).